Precise binocular eye alignment is required to have single binocular vision and stereoscopic depth perception. The alignment of the two eyes is the result of orbital mechanics, "hard wiring" (neural elements not affected by adaptation), and adaptive mechanisms that keep binocular yoking precise despite changes in the oculomotor system that may occur because of development, aging, disease or trauma. Adaptive tonic vergence is particularly necessary for vertical and torsional vergence which, unlike horizontal vergence, are not under voluntary control. Our past experiments have dealt with vertical ocular alignment, but in order to obtain precise alignment of images on binocular corresponding points of the retina, the eyes must be aligned horizontally, vertically and torsionally. The present program of experiments will examine the torsional component of eye alignment in relation to eye and head position in adapted and in unadapted states. These studies will reveal the baseline relationship between torsion and eye position in the absence of short term adaptation, and the duration of adapted responses. We will explore the relationship between torsion and horizontal and vertical disparity vergence and vertical phoria adaptation. We will also investigate the capacity of torsional eye movements to adapt to visual stimuli that mimic naturally occurring errors in binocular eye alignment and otolith disorders. These experiments should provide a wealth of information on the normal coordination of 3-dimensional eye movements and provide a basis for clinical research in this area.